For example, according to Japanese Unexamined Patent Publication No. Hei 6-181028, there has been disclosed a cord type thermal fuse, comprising a space layer and an insulating cover layer around a center core member, on which a conductor meltable at a predetermined temperature is wound in the lateral direction on an elastic core. There are lead wires connected to the both ends of the conductor via terminals, and when the conductor melts at excessive temperature the electric connection between the lead wires is cut, whereby the abnormal state is detected.
According to Japanese Unexamined Patent Publication No. Hei 7-306750, there has also been disclosed a cord type thermal fuse, substantially having the same structure.
According to Japanese Unexamined Patent Publication No. 2000-231866, there has been disclosed a cord type thermal fuse, wherein a core wire, comprising a metal wire meltable at a predetermined temperature, is wound in the lateral direction with predetermined intervals on a core member and is inserted into a protection tube. The protection tube comprises a glass braid sleeve covered by an extruded silicone rubber.
With regard to these cord type thermal fuses, to promote the flow of the melted conductor or the metal wire during opening of the fuse, so as to improve the detecting accuracy, flux was applied to the conductor or the metal wire.
However, according to these types of cord type thermal fuses, since there have been high-integration of structure of combustion apparatus, the thermal ambience during long-term use becomes severer. Thus, the deterioration of flux would be prompted due to aging by heat, or the reliability of conductor would be lowered by heat, and it should be foreseen that a quick response to temperature would not be obtained after deterioration due to thermal aging.
Although attempts have been made to improve reliability for example, according to the cord type thermal fuse of Japanese Unexamined Patent Publication No. 2000-231866, there has been disclosed, as means to solve the problem, only the silicone rubber material, of which mechanical strength is normally low, and which requires reinforcing means as an exterior element. Thus, when the protection tube is ripped and damaged by edges, etc. of metal parts inside the combustion apparatus, there would be a higher risk of electric leakage by intrusion of water, and also a higher risk of prompted deterioration of flux due to aging by intrusion of exhaust gas.
In light of the above problems, it is an object of the present invention to provide a cord type thermal fuse, which can be disconnected when any part thereof is exposed in an abnormal high temperature state, so that the abnormal temperature can be detected accurately, in particular, of which disconnection time is still good even after being deteriorated due to aging by heat, and also to provide a sheet type thermal fuse, substantially having the same characteristic as that of the cord type thermal fuse as mentioned above.